Fine structural aspects of the development of Ito cells (vitamin A uptake cells) in chick embryo livers.

The development of Ito cells in the chick embryo liver was studied using electron as well as fluorescence microscopes. The collagen fibrils in the Disse's space can already be seen in 6-day-old chick embryos. This space contains fibroblast-like cells which should be called primitive Ito cells. They are slender cells characterized by numerous free polyribosomes. The rough endoplasmic reticulum, Golgi apparatus and 10 nm microfilaments are also well developed. The fluorescence of vitamin A and lipid droplets begin to appear in the primitive Ito cell at 9 days of incubation in both the control and vitamin A-treated animals. A special topographic relation between the lipid droplets and cell organelles is difficult to recognize. The primitive Ito cell in the Disse's space acquires the ability to produce collagen fibrils earlier than that of taking up and storing vitamin A. The Ito cells containing lipid droplets increase in number with embryonic age, and about 40-50% of perisinusoid cells have droplets of vitamin A at 21 days of incubation. The droplets are usually less than 1 micron in diameter and do not fuse with each other.